function. All of these roles could provide
ergogenic potential, but the most researched
theory involves the effect of phosphate salt sup-
plementation on 2,3-DPG levels. Increased levels
of 2,3-DPG could facilitate release of oxygen
from haemoglobin in the red blood cell and
possibly enhance aerobic endurance exercise
performance.
efficacy
Current research is equivocal as to whether or
not phosphate loading may improve physiologi-
cal functions important to endurance per-
formance. About a dozen studies have been
conducted. No study has reported decreases in
performance, and four well-controlled studies
(Cadeet al. 1984; Kreider et al. 1990, 1992; Stewart
et al. 1990) have reported that phosphate supple-
mentation may enhance exercise performance.
However, the underlying mechanism has not
been clarified. For example, 2,3-DPG did not
increase in all studies. Increased maximal oxy-
gen uptake and improved performance on cycle
ergometer exercise tests are the most consistent
findings. Although these results are impressive, a
number of confounding variables in previous
research have been identified and more con-
trolled research has been recommended
(Tremblay et al. 1994).
safety
Phosphate supplements may cause gastrointesti-
nal distress unless consumed with ample fluids
or food. Chronic consumption, particularly with
limited calcium intake, can lead to a decreased
calcium to phosphate ratio, which may increase
parathyroid hormone secretion and impair
calcium balance.
L-Carnitine
theory
Carnitine, a non-essential short-chain carboxylic
acid, is a vitamin-like compound found naturally
360 nutrition and exercise
in animal foods but may also be synthesized in
the liver and kidney. l-Carnitine is the physio-
logically active form in the body and has been
the form most commonly used as a dietary
supplement.
l-Carnitine may affect various physiological
functions important to exercise; most of the
effects are ergogenic in nature but some may
possibly impair performance, i.e. be ergolytic
(Wagenmakers 1991; Williams 1995). A primary
function of l-carnitine is to facilitate transfer of
free fatty acids (FFA) into the mitochondria to
help promote oxidation of the FFA for energy.
Theoretically, l-carnitine supplementation could
enhance FFA oxidation and help to spare the use
of muscle glycogen, which might be theorized toFig. 26.2Theoretically, nutritional ergogenic aids may
enhance physiological or metabolic processes deemed
important for aerobic energy production. Photo ©
Allsport / Martin.